DESCRIPTION: One critical component of normal visual behavior is the ability to find a target stimulus in a visual field containing multiple distracting stimuli. The proposed experiments fall into two groups. One examines what attributes of the stimulus are critical for efficient search, and the other asks where in the visual field those attributes can be processed. Search for almost any stimulus is harder in the periphery. These changes in performance with eccentricity are not fully explained by the well-studied decreases in acuity and sensitivity with eccentricity. The investigator plans to investigate what underlies the substantial eccentricity effects in visual search and explain the impact of visual and non-visual stress on such mechanisms. These "Useful Field of View" effects are known to be more marked in older Ss and have been shown to correlate with driving accidents. The investigator plans to simulate several natural visual stressors to examine their impact on the Useful Field of View. The second, what, aspect of the project is concerned with the relationship of search performance to the properties of the stimuli. Visual search is poised at a bottleneck in visual processing. Early stages of processing are largely parallel with all stimuli processed at once. In later stages, only a restricted region can be processed at one time. The parallel stage has been thought to be limited to the processing of a few basic features. However, recent data leads to the conclusion that parallel processes relatively early in the visual pathway accomplish a division of the stimulus into potential search items or objects. The PI plans to investigate the existence of an "item map" in the parallel stages of visual processing. This research will expand our understanding of those behaviors, from driving to radiology, that require visual search.